A MOI newby challenge that I don't know how to fix : )
Having made it, I realised the highlighted tapered section should be lower in position - all other elements are OK.
Info palette confirms it's a solid to start with. I tried separating those faces, moving them down, selecting the open edges and making a straight loft to fill the gap (open), then rejoining everything. I end up with 'joined surfaces' :(
One way is to copy the oval edges to the desired separation, which become oval curves.
Extrude the oval curves away from each other, without capping ends.
Then hide the curves. Select the new oval edges, and do Blend with minimal bulge ( = 0).
Planar the two Blend ovals and Join the 4 parts.
Normally Bridge kills automatically the bottom face !
when you Bridge a face from a solid volume to an "alone face" (not from another volume)
or a face from another subdivised surface! (not the case here ! )
So no need to Bolean Union !
But here it's a trimed face so boolean Union is needing!
Perhaps a classic error when you loft in your your first try was to have made à caped loft.
You don't see the cap but moi don't know how to join for this case.
Yep i use only SimLab (because it's very easy and permit to mix many 3D formats in the same time ) in free that is now 1920*800
or even SketchUp format! So no problem of regulate : you can play with smaller etc... if you have complex volume...
example with a model by thegoodguy
I have not made any special regulates (that was just for a test :)
Here SketchUp export from Moi : as you see you are not obliged to use OBJ format :)
A trick : export different objects against all in one if there are several complex objects!
You have another very cool free one (if you had loaded it previous year) : TwinMotion ! Without any limitation!
Updates are free too!